576 FILICALES 
The shoot is sometimes upright and radial, with leaves showing 2ths 
phyllotaxis, as in some species of TZ?zchomanes; or more commonly 
creeping and dorsiventral, with the leaves arranged distichously, with 
elongated internodes, as in many species of TZyichomanes, and all of 
Hymenophyllum. From the axis numerous scattered roots arise in most 
species, but in some, and especially in the section Memzphlebium of 
Trichomanes, no adventitious roots are formed, leafless branches of the 
rhizome serving as substitutes. These are covered by root-hairs, which 
resemble, however, the hairs which are normally found on axis and leaf 
in the rooted species also. The hairs are filamentous, and ramenta are 
absent, but peculiar scales are found in some species of Z+ichomanes, and 
in some of Aymenophyllum of exposed habit the leaf is covered with 
a hairy felt. 
The leaves in some of the larger species (77. dilatatum, australe) conform 
in outline to ordinary branched Filicinean types, and are winged structures 
to the base (Fig. 322). But in other cases the leaf may appear as a 
widened expansion of simple form, with or without a leaf-stalk (Fig. 323), as 
in 4. cruentum, or.T. rentforme, and membranaceum. It would appear probable 
that the latter are specialised and derivative forms, and they occur more 
freely in the genus Z7ichomanes, which there is good reason to believe to 
be the more specialised genus. The leaves are translucent or “filmy” 
in texture, a feature that will be considered at length below. 
Axillary branches occur very generally in the Hymenophyllaceae, but 
at many nodes the rudiment of the axillary bud remains undeveloped. 
The sori are marginal in all cases: the receptacle upon which the 
sporangia are inserted in strictly basipetal sequence is traversed by the 
direct continuation of one of the veins of the lamina; it is surrounded 
by the cup-like indusium, which is entire in Z+ichomanes, but two lipped 
in Aymenophyllum. Theesporangia vary greatly in size and productiveness, 
but have uniformly an oblique annulus and lateral dehiscence: it will 
be seen that these characters are closely related to the regular basipetal 
sequence in which they are produced npon the receptacle. 
Sori and sporangia of corresponding type have been traced back to 
early geological formations. From the upper Carboniferous, or perhaps 
even earlier, come the doubtful sporangia of Hymenophyllites, which will be 
considered in detail below. Meanwhile it may be noted that there is 
reason to believe the type to have been a very, ancient one. 
SPORE-PRODUCING MEMBERS. 
The comparative study of the sorus of the Hymenophyllaceae leads 
to the conclusion that while these Ferns show the highest complexity 
of the receptacle, the sporangia themselves are related in character 
to more massive types, and that this will justify a systematic position 
near to the lLoxsomaceae, Dicksonieae, and Gleicheniaceae on the 
